Field of the Invention
The present invention relates to a detection technology, particularly to a method and a device for detecting conduction mode.
Description of the Related Art
Switching power converters with synchronous rectification utilize switching between inductor's current continuous and discontinuous conduction operation modes (CCM and DCM) in order to achieve improved power efficiency across wide load and input voltage ranges. The inductor current zero crossing is sensed in order to detect the operation modes transition point between CCM and DCM. The challenges associated with this include inductor current zero crossing point sensing accuracy, noise effect near the zero crossing point and the sensing circuitry speed and power loss.
While synchronous rectification is used in switching power converters in order to improve the power efficiency at high load currents in addition to reducing the output voltage ripple, transitioning from CCM to DCM at lighter load currents is used in order to improve light load power efficiency. Switching from CCM to DCM or vice versa requires sensing the zero crossing of the inductor current. This requires sensing the instantaneous inductor current information at the switching frequency speed, its accuracy and stability is sensitive to noise effect at the zero crossing transition point and it results in additional power losses by the sensing circuitries especially at higher load currents and at higher switching frequencies. The detection of the inductor current zero crossing, which determines the operation mode (CCM or DCM) and determines the Synchronous Rectifier (SR) switch turn off time in DCM, requires sensing the instantaneous current of the output inductor, where the high bandwidth sensing and detection circuitries are essential in order to detect the correct zero crossing point. Moreover, the switching noise, which is introduced at the instances of turning ON and OFF of the converter switches (where the zero crossing of inductor current occurs), makes it more difficult to detect the zero crossing time (and the non zero crossing) accurately.
To overcome the abovementioned problems, the present invention provides a method and a device for detecting conduction mode, so as to solve the afore-mentioned problems of the prior art.